Middle-aged men who drink alcohol only occasionally appear to reduce their risk of developing type 2 diabetes by increasing their alcohol consumption to about one to two servings a day of beer, wine or liquor, according to a new study by researchers at Harvard School of Public Health (HSPH) and scientists in the Netherlands.

“Changes in one’s alcohol consumption pattern over time have a subsequent influence on one’s type 2 diabetes risk,” said lead author Michel Joosten of Wageningen University in the Netherlands, who conducted the study while a visiting scientist at HSPH. The Netherlands Organization for Applied Scientific Research(TNO) also participated in the study. “Occasional drinkers who increase their intake to moderate levels – say one to two drinks a day — reduce their type 2 diabetes risk,” Joosten said. Conversely, if moderate drinkers lower their intake over time, their type 2 diabetes risk increases and becomes comparable to initial occasional drinkers. No further risk reduction was seen when the men increased their intake beyond two drinks a day.

The study appeared in the January, 2011 issue of the American Diabetes Association journal Diabetes.

“By no means do we interpret this data to say that people should take up drinking to reduce their risk of type 2 diabetes. However, it does give us some insight into mechanisms of action for the benefits of moderate alcohol consumption,” said senior author Eric Rimm, associate professor in the Departments of Epidemiology and Nutrition at HSPH. “The growing body of evidence is strong enough to suggest that an individual who is at risk of type 2 diabetes should change their lifestyle to lose weight, increase their exercise and eat a healthy diet. Our results strongly suggest that a healthy diet can include moderate alcohol consumption,” Rimm said.

About the study

The researchers examined data on 38,031 middle-aged American men enrolled in the Health Professionals Follow-Up Study (HPFS) over a 20-year period from 1986 to 2006. Alcohol use was tracked on food questionnaires every four years. The men studied were free of type 2 diabetes (and cancer) in 1990. A total of 1,905 cases of type 2 diabetes occurred during the study.

The study investigated how four-year changes in alcohol consumption affected the risk of type 2 diabetes over the next four years. About 75% of the men remained fairly stable in their consumption pattern. An increase in intake to moderate levels over four years was associated with a 25% lower risk of type 2 diabetes among initial light drinkers.

U.S. Department of Agriculture serving guidelines were used to calculate the amount of beer, wine and liquor consumed by the HPFS participants. Current USDA guidelines consider moderate drinking for men as no more than two drinks a day and for women, no more than one drink a day. A drink is 12 ounces of regular beer, 5 ounces of wine, and 1.5 ounces of 80-proof distilled spirits.

The researchers discuss a number of potential physiological mechanisms for how alcohol might reduce diabetes risk. They found indications that increased alcohol consumption to moderate levels was associated with improved Hemoglobin A1C levels, a measure of the average blood glucose level over the past two or three months. Like previous studies by others, the researchers found alcohol increased adiponectin levels, a hormone that improves insulin sensitivity, protecting against type 2 diabetes.

In addition to alcohol, the researchers considered other factors that may influence diabetes risk, including weight, physical activity, smoking habits and diet.

The Health Professionals Follow-up Study is supported by the National Institutes of Health. Additional funding was provided by Stuurgroep Alcohol Research in The Hague, the Netherlands.